This invention relates to devices for draining fluids from a tubing string in a hydrocarbon production well. Tubing drains allow fluids to drain from the tubing string of a well. Among other purposes, draining fluid from the tubing string allows the tubing to be removed from a well without pulling the tubing “wet”, which occurs when there is an obstruction in the tubing which prevents the fluid from draining out of the bottom of the tubing. For example, if the well is produced with a rod pump and the rods have parted leaving a pump or plunger at the bottom of the tubing string, the tubing will stand full of fluid requiring the well to be pulled wet, unless a drain can be actuated which allows the fluid to escape from the inside of the tubing into the casing-tubing annulus. Pulling the tubing wet can result in produced fluid being spilled on the ground surface as well as potentially spraying the production rig crew as the tubing joints are unscrewed. Such releases may violate a variety of laws and regulations, including those pertaining to environmental protection and occupational health and safety.
Tubing drains are typically operated either by manipulation of the tubing, usually by rotation, or by applying pressure to the tubing string to a sufficiently high pressure to burst one or more rupture disks or pins contained within the tubing drain. In either case, once the drain is opened, the tubing must be pulled to the surface so that the drain may be refurbished with the replacement of the rupture disks or pins.
The drains which are activated by rotating the tubing typically utilize a plug located in the body of the drain which is dislodged when the tubing is rotated. The dislodged plug allows the tubing to drain through the resulting open port. The plug is typically propelled out of the drain body falling downhole, which means that once the drain is activated it cannot be closed. In other words, once the plug is out, the tubing drain and tubing must be pulled out of the hole and the drain serviced to replace the plug.
Drains which are actuated by application of tubing pressure are the most commonly used. These drains utilize hydraulically actuated rupture disks or pins and require the application of pressure to the tubing at the surface. Once the pressure at the tubing drain reaches a certain pressure, the disk or pins rupture. As the fluid drains from the tubing, the respective fluid levels in the tubing and in the casing-tubing annulus equalize. Like the tubing drain described above, which is actuated by tubing manipulation, the drains which utilize rupture disks and pins can only be used one time and thereafter the drain must be pulled out of the well to be serviced with the installation of new rupture disks or pins.
The hydraulically actuated drains have a further disadvantage in that the drains can be inadvertently actuated. In such cases, the production equipment—usually comprising a rod string, downhole pump, and tubing string—becomes inoperable and must be removed to change out the hydraulic drain. Unintentional rupturing of the disk or shear pins can be caused, of course, by the pressuring up of the tubing by some event, such as the accidental closing of a valve on a surface production line. However, other phenomena may also rupture the disk or shear pins. For example, the movement of rod couplings within the tubing string presents a potential mechanism for rupturing the disk. Physical contact between a rod coupling and the disk can cause rupturing of the disk by the impact by the coupling upon the disk. In addition, the motion of the coupling in close proximity to the hydraulic drain can cause a localized pressure spike resulting from the piston effect of the coupling inside or adjacent to the drain. The likelihood of such premature rupturing of the disk increases with the decrease in clearance between the rod coupling and the inside diameter of the hydraulic drain.
Another disadvantage of some hydraulic drains is that the rupture disks or pins are often uncontained when ruptured such that the disk or pin remnants end up inside the well, leaving junk/trash which can either interfere with the operation of downhole equipment or which can accumulate with other debris to create a wellbore obstruction.
Another disadvantage of both the hydraulic and mechanical drains described above is that there are occasions when a well problem might otherwise be resolved without pulling the tubing. However, once the tubing drain is activated, it becomes necessary to pull the tubing and the tubing drain to refurbish the drain. In all such occurrences, pulling the tubing string is expensive because of the required crew and equipment and also because of the resulting loss of hydrocarbon production lost while the well is inactive.
As illustrated by the disadvantages described above, there are benefits to be gained if pulling the tubing string for servicing of the drain can be avoided by a tubing drain which is capable of being resealed in situ following activation of the drain.